A nonlinear optimal control approach to reduce travel times and to improve safety in freeway traffic systems

This work addresses the problem of controlling freeway traffic systems with coordinated ramp metering, by taking into account not only the reduction of travel times for the drivers but also the improvement of safety conditions. Specifically, a coordinated ramp metering control strategy is sought by defining and solving an optimal control problem in which the objective function to be minimized is a weighted sum of the total time spent and the expected number of crashes. The resulting problem is a finite-horizon nonlinear optimal control problem with constrained control variables. It is solved by applying the feasible direction algorithm, in the specific version adopting the derivative backpropagation method RPROP. The simulation results show the effectiveness of the proposed method both in reducing the total time spent by the drivers and in increasing safety conditions.